1. Field of the Invention
The present invention relates to a noncontact integrated circuit (IC) card, and more particularly to a noncontact IC card restricting the amount of electric power consumed while waiting to receive signals.
2. Description of the Related Art
In recent years, a noncontact IC card, which does not have an external electrode on the surface thereof, has been the most remarkable among the many kinds of IC cards produced. Though the noncontact IC card transmits and receives signals to and from an external device in the same manner as a normal IC card which has an external electrode, the transmission and receiving are performed by using a space transmission medium, such as electromagnetic waves, light, magnetism and so on.
A structure of a conventional noncontact IC card is shown in FIG. 5. A ROM 2 and a RAM 3 are connected through a bus 8 to a CPU 1 which controls operation of the IC card. Connected to the bus 8 is an input-output control circuit 4 which controls input and output of data to and from an external device and is connected to the input-output control circuit 4 through a modem circuit 5 and an antenna 6. Furthermore, a battery 7 is contained in the IC card so as to supply electric power to each electric circuit.
In such an IC card, if the antenna 6 receives a request signal in the form of electromagnetic waves from the external device, the request signal is input to the CPU 1 through the input-output control circuit 4 after being demodulated in the modem circuit 5. The CPU 1 decodes the request signal and produces a predetermined response signal. The response signal is input to the modem circuit 5 through the input-output control circuit 4, modulated, and then transmitted to the external device from the antenna 6.
However, it is required that the CPU 1, the modem circuit 5 and so on always be operated on standby so that the IC card can receive and processes the request signal from the external device. Therefore, electric power is always being consumed in order to operate the CPU 1, the modem circuit 5 and so on, and this causes a problem in that the electric power supplied by the contained battery 7 is rapidly consumed.